Electrical Troubleshooting Quiz, March 23, 2010

Your boss, eager to have it fixed, schedules a shutdown for you to conduct insulation resistance tests. In parallel with this, your boss has a crew of mechanics coming in to ensure the connections are good. What should you tell your boss?

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An odd discrepancy exists on all of the feeders. Each feeder is busway. On each one, voltage drop (which, by definition, is a calculation) shows one value, but actual measurement shows a much higher value. This means energy waste.

Your boss, eager to have it fixed, schedules a shutdown for you to conduct insulation resistance tests. In parallel with this, your boss has a crew of mechanics coming in to ensure the connections are good. What should you tell your boss?

There is a standard, highly effective technique for solving this disparity, which we'll discuss in a moment.

First, your boss needs to read Art. 90 of the NEC, plus the OSHA requirements pertaining to "qualified worker." Mechanics should never work on electrical power distribution equipment unless they have been specifically qualified on it. If they "ensure all of the connections are good," exactly how will they do this? Most likely, they’ll take wrenches to existing good joints and turn them into bad joints.

When tightening connections in bus systems, don't use a torque chart. Instead, use the bus manufacturer's specifications, as this is an engineered system. Never adjust an existing connection without taking it apart, cleaning it, and then reassembling it with new hardware.

Insulation resistance tests are great for cables, but are not of primary benefit for identifying losses on busway. The standard technique for solving this disparity is the infrared analysis. A certified thermographer can save you time and money by mapping precisely where the voltage losses are occurring. Usually, losses occur at connections that need to be redone. So, unschedule the mechanics, and schedule a thermographer.

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